1. Technical Field of the Invention
The present invention generally relates to a method and apparatus for automatically generating solid models and to a computer readable storage medium storing programs for automatically generating solid models, and more particularly, to a method and an apparatus for automatically generating a solid model from a plurality of plan views such as front, side, top and bottom views, and to a computer readable storage medium which stores a program for automatically generating a solid model by use of the method.
2. Related Art
Three plan views selected from views such as front, side, top and bottom views are often used to describe a three-dimensional object. By use of such plan views, the three dimensional object can be described using a three-dimensional computer aided design (CAD) system.
However, it requires complicated operations to input necessary information to the CAD system, and there are demands to automatically generate a three-dimensional object from three plan views.
Conventionally, there is a first technique which automatically generates a three dimensional object, that is, a solid model, from three plan views. This first technique obtains candidates of apexes from the three plan views, and then obtains candidates of edge lines from the candidates of the apexes. A wire frame model is generated based on the candidates of the apexes and the candidates of the edge lines. Next, a surface model having surfaces surrounded by the edge lines is generated. Finally, a solid model is generated by determining which side of each surface of the surface model the object exists.
On the other hand, there is a second technique which prepares within a system basic shapes such as a parallepiped, cylinder and cone shapes. This second technique retrieves loops or closed sequences of line segments in each of the three plan views. Then, a correspondence among the retrieved loops in each of the plan views is obtained, so as to successively create the basic shapes.
According to the first and second techniques described above, it is a precondition that the geometrical shape is strictly drawn on the three plan views. But in actual mechanical drawings, simplified drawings including the following simplifications are used as the base.
(1) Complicated interpenetrating lines are approximated by straight or arcuate lines; and PA1 (2) Shapes and the like of tools and jigs used for the process are only drawn by imaginary lines, and edge lines which are generated as a result are omitted.
The three plan views including the simplifications (1) and (2) described above are mainly used to process and produce the object. In addition, machine tools such as lathes and milling machines are used to process surfaces of the object. On the other hand, information that is accurately drawn on the three plan views relates to the shape of the surfaces and not to the shape of the edge lines. For these reasons, there was a problem in that it is impossible to generate a correct solid model according to the first technique or the second technique described above.